1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to an LCD bonding apparatus and method for fabricating an LCD incorporating a liquid crystal dispensing method applied thereto.
2. Discussion of the Related Art
In general, recent developments in the information communication field have increased demand for various types of display devices. In response to this demand, various flat panel displays such as liquid crystal display (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent display (VFD) have been developed, some of which have been employed as displays in various products.
The LCDs have been used most widely as mobile displays. The LCD has replaced the CRT (Cathode Ray Tube) because of features and advantages including excellent picture quality, light weight, thin profile, and low power consumption. In addition to the mobile type LCDs, such as a display for notebook computer, LCDs have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in the LCD technology with applications in different fields, research in enhancing the picture quality of the LCD as a display has been in some respects lacking as compared to the features and advantages of the LCD. Therefore, to use the LCD in various fields as a general display, the key to developing the LCD lies on whether the LCD can provide a high quality picture, such as high resolution, high luminance, and large sized screen, while still maintaining light weight, thin profile, and low power consumption.
An LCD device includes a liquid crystal panel for displaying a picture and a driving part for providing a driving signal to the liquid crystal panel. The liquid crystal panel has first and second glass substrates bonded together with a gap between the substrates. A liquid crystal layer is formed by injecting liquid crystal into the gap between the first and second glass substrates.
On the first glass substrate (a TFT array substrate, for example), there are a plurality of gate lines arranged in a first direction at fixed intervals, a plurality of data lines arranged in a second direction perpendicular to the gate lines at fixed intervals, a plurality of pixel electrodes in respective pixel regions defined by the gate lines and the data lines in a matrix, and a plurality of thin film transistors switchable in response to a signal from the gate lines for transmission of a signal from the data line to the pixel electrodes.
The second glass substrate (a color filter substrate) has a black matrix layer for shielding light from areas excluding the pixel regions, red (R), green (G), blue (B) color filter layers, and a common electrode for implementing a picture.
The foregoing first and second substrates have a gap between them which is maintained by spacers. The first and second substrates are bonded to each other by a sealant. The seal has a liquid crystal injection inlet through which liquid crystal is injected after the two substrates are bonded and sealed.
After the individual liquid crystal panels are cut, the space between the two bonded substrates of each LCD panel is evacuated and the liquid crystal injection inlet is dipped in a liquid crystal bath, so that the liquid crystal is injected into the space by a capillary tube phenomenon. Once the liquid crystal is injected into the space between the two substrates the liquid crystal injection inlet is sealed by a sealant.
However, the related art method for fabricating an LCD having liquid crystal injected therein has the following problems. First, the related art method has poor productivity because the dipping of the liquid crystal in a liquid crystal bath while the space between the two substrates are maintained at a vacuum and the unit panels are cut into individual pieces for injection of the liquid crystal takes much time. Second, the liquid crystal injection, for a large LCD in particular, may cause imperfect filling of the liquid crystal in the panel, which may result in a defective panel. Third, the complicated and lengthy fabrication process requires the use of many liquid crystal injection devices, which occupies a large portion of space.
Accordingly, a method for fabricating an LCD by using a liquid crystal dropping method has been under research recently. Japanese Patent Application Nos. H11-89612, and H11-172903, and Japanese Laid-Open Patent Publication No. 2000-147528 disclose the following liquid crystal dropping method.
FIGS. 1A-1D illustrate a related art bonding machine having the liquid crystal dropping method applied thereto. FIG. 2 illustrates a perspective view showing a state of operation of key parts of substrate receiving means in a related art bonding machine, schematically.
The related art LCD bonding machine (e.g., substrate assembler) is provided with a frame 10, stage parts 21 and 22, a sealant outlet (not shown), a liquid crystal dropping part 30, chamber parts 31 and 32, chamber moving means, substrate receiving means, stage moving means, and evacuating means.
The stage parts include an upper stage 21 and a lower stage 22. The sealant outlet and the liquid crystal dropping part 30 are fitted to the outside of the frame 10.
The chamber parts include an upper chamber unit 31 and a lower chamber unit 32. The upper chamber unit 31 has a vacuum valve 23 and a hose 24 connected thereto for evacuating the chamber parts, and a gas purge valve 80 and a gas tube 81 for turning the chamber parts from a vacuum state to an atmospheric pressure state.
The chamber moving means has a driving motor 40 for selective movement of the lower chamber unit 32. That is movement of the lower chamber unit 32 to a location (S2) where the bonding may occur or to a location (S1) where the coating of the sealant and dropping of the liquid crystal may occur.
The substrate receiving means for temporarily receiving opposite diagonal positions of the second substrate 52 and when the interior of the chamber is in vacuum and is attached and fixed to the upper stage 21.
The substrate receiving means has a rotatable shaft 61 passing from the outside chamber unit 31 to the interior of chamber unit 31. A rotation actuator 63 fixed to the outside of an upper part of the chamber unit 31, one end of the rotating shaft 61, for selective rotation of the rotating shaft 61, an elevating actuator 64 fixed to an outside of an upper part of the chamber unit 31 for selective elevation of the rotating shaft 61, and a supporting plate 62 formed as one unit with the rotating shaft 61 at the other end thereof for selective supporting of corners of the substrate.
The stage moving means has a shaft 71, a housing 72, a linear guide 73, a motor 74, a ball screw 75, and a nut housing 76. That is, the upper stage 21 is supported on the shaft 71 and the shaft is fixed to the housing 72. The housing 72 is fitted to the frame 10 by the linear guide 73. The upper stage 21 is moved up/down by the motor 74 fixed to a bracket 77 on frame 10. In this instance, the ball screw 75 and the nut housing 76 transmit a driving power, and the nut housing 76 is connected to the housing 72 through a load gauge 78.
The steps of a method for fabricating an LCD by using the foregoing related art bonding machine will be explained following an order of the fabrication process in detail.
Referring to FIG. 1A, the second substrate 52 in a carrier is placed on the lower stage by a robot arm 90. Next, the second substrate 52 is moved toward the upper stage 21 by the driving motor 40 positioned in the chamber moving means.
Referring to FIG. 1B, the upper stage 21 biases the second substrate 52 by vacuum. Next, the lower chamber unit 32, having the lower stage 22, is moved to location (S1) for coating sealant and dropping liquid crystal by driving the driving motor 40.
Then, referring to FIG. 1C, the first substrate 51 is placed on the lower stage 22 by the robot arm 90 and connected to the lower stage 22 by vacuum.
Referring to FIG. 1D, after the sealant coating and the liquid crystal dropping have been applied to the first substrate 51 by the sealant outlet and the liquid crystal dropping part 30, the chamber moving means 40 moves the lower chamber unit 32 to location (S2).
Next, the chamber moving means 40 unites the chamber units 31 and 32, thereby, enclosing a space where the stages 21 and 22 are placed so that the space can be evacuated with the vacuum valve 23 and the hose 24.
Since the vacuum of the space becomes higher than the vacuum applied to the upper stage 21, which holds the second substrate 52. Temporary safekeeping of the second substrate 52 is required before the space is fully evacuated in order to prevent the second substrate 52 from falling and/or breaking.
The elevating actuator 64 is driven to move the rotating shaft 51 toward the under side of the upper stage. In addition, the rotating actuator 63 is driven to rotate the rotating shaft 61 for placing a supporting plate 62 on two corners of the second substrate 52 connected to the upper stage 21 via a vacuum.
The stage moving means moves the upper stage 21 down to a location close to a height of the supporting plate 62 in which the substrate receiving means is located and releases the vacuum that holds the second substrate 52, in order to place the second substrate 52 on the supporting plates 62 as shown in FIG. 2.
When the chamber is fully evacuated, the second substrate 52 is held to the upper stage 21 by static electricity applied thereto. Subsequently, the rotating actuator 63 and the elevating actuator 64 are driven, bringing the supporting plates 62 and the rotating shaft 61 to their original positions where the bonding will not be interfered with.
Under the vacuum state the motor 74 is driven to move down the upper stage 21 thereby pressing the substrates 51 and 52 together.
In this instance, a preset pressure is applied as required for bonding by controlling the motor 74 with reference to pressure signals. That is, feed back pressure signals are used to ensure appropriate application of pressures. The load gauge 78 serves as a load cell (pressure application sensor).
FIGS. 3A-3F schematically illustrate sections showing the steps of a related art method for fabricating an LCD having the liquid crystal dropping method disclosed in Japanese laid-open patent publication No. 2000-147528 applied thereto.
Referring to FIG. 3A, ultra violet (UV) sealant 1 is coated on a first glass substrate 3 having thin film transistor arrays formed thereon to a thickness of approximately 30 μm. The liquid crystal 2 is dropped on an inner side of the UV sealant 1 where there is a thin film transistor array. No liquid crystal injection inlet is provided in the sealant 1.
The first glass substrate 3 in a vacuum chamber is mounted on a table 4, which is movable in a horizontal direction. A first vacuum channel 5 holds the entire bottom surface of the glass substrate 3.
Referring to FIG. 3B, the entire bottom surface of the second glass substrate 6 having the color filter arrays formed thereon is held by vacuum channels of 7 and the vacuum chamber is closed and evacuated. The second table is moved down in a vertical direction until a gap between the first and second glass substrate 3 and 6 is 1 mm. Table 4 with the first glass substrate 3 is moved in a horizontal direction to pre-align the first and second glass substrates 3 and 6.
Referring to FIG. 3C, the second table is moved down until the second glass substrate 6 comes into contact with the liquid crystal 2 and/or the sealant 1.
Referring to FIG. 3D, table 4 with the first glass substrate 3 is moved in a horizontal direction to align the first and second glass substrates 3 and 6.
Referring to FIG. 3E, the second table is moved down in a vertical direction until the second glass substrate 6 comes into contact with the sealant 1. In addition, the second table is pressed down until a gap between the second glass substrate 6 and the first glass substrate 3 becomes approximately 5 μm.
Referring to FIG. 3F, the bonded first and second glass substrates, 3 and 6 respectively, are taken out of the vacuum chamber and a UV ray is applied to the sealant in order to harden the sealant 1, thereby completing the fabrication of the LCD.
The foregoing related art vacuum bonding machine and method for fabricating an LCD having the liquid crystal dropping method applied thereto has the following problems.
First, the use of only one vacuum means creates difficulty in adjusting the evacuation rate. In particular, it is desirable that the interior of the chamber is evacuated faster in order to reduce the fabrication time period. However, the use of a vacuum means that can form a high vacuum (e.g., generating a high air suction power) causes defective amount of liquid crystal on the substrate, thereby causing a defective product. That is, the volatility of the liquid crystal becomes greater as the vacuum becomes higher. For example, a rapid evacuation of the interior of the bonding chamber may cause more violent volatilization, thereby creating a defective liquid crystal amount on the substrate.
Second, the use of a vacuum pump that forms a low air suction power for solving the foregoing problem requires a large amount of time for evacuating the interior of the chamber.
Third, rapid introduction of air into the process chamber when the vacuum state is changed may lead the upper or lower stage to become stuck to one of the substrates. This affects the atmospheric state bonding of the substrates significantly and may cause defective bonding.
Fourth, defective sealing between the lower chamber unit and the upper chamber unit when the two pieces are united can occur as a result of the two-pieced chamber parts. In particular, difficulty arises in forming a tight seal and may create vacuum leaks, which can prevent the desired degree of bonding due to difficulty in obtaining a high vacuum in the interior of the chamber.
Fifth, the supporting of corner parts of the substrate by the substrate receiving means may cause bending or warping of the substrate when the substrate is large and/or may cause the substrate to break and fall down from the substrate receiving means.
Sixth, the sealant coating and liquid crystal dropping on the same substrate require a lengthy fabrication time period before the two substrates are bonded.
Seventh, as the sealant is coated and the liquid crystal is dropped on the first substrate, no progress is made for the second substrate. Thereby, resulting in an imbalance of fabrication processes between the first and second substrates creating an ineffective operation of the production line.
Eighth, the first substrate has the sealant and liquid crystal applied, therefore, it can not be subjected to cleaning by ultra-sonic cleaning (USC). Therefore, particles can not be removed as the USC is not applied, and this may cause defective contact of the sealant in the bonding process.